Structural health monitoring seeks to determine the health of structures, typically by employing sensors/actuators distributed upon a structure. Actuators commonly query the structure, and sensors detect these querying signals, whereupon the detected signals are analyzed to determine whether any defects (e.g. cracks, pits, delaminations, etc.) or signs of failure have developed. It is often desired that these monitoring systems be capable of operating in a nondestructive manner (i.e. that the systems be capable of monitoring structures without causing any damage to them), and operating while the structure itself is undergoing normal operations.
However, such nondestructive monitoring is challenging when the structure operates in, or generates, an extreme environment. For example, the monitoring of structures such as liquid propellant rocket engines is often desired, as high operating stresses make devastating and dangerous structural failures more likely. However, these structures also generate harsh operating conditions that pose great challenges to implementation of monitoring systems. In particular, monitoring systems must be able to simultaneously withstand both cryogenic temperatures (typically, the temperatures at which liquid propellant such as liquid oxygen or liquid hydrogen is stored) and the high vibrations generated by engine operation. Accordingly, it is desirable to develop structural health monitoring systems capable of operating in cryogenic, high vibration environments.
Furthermore, the harsh conditions presented during operation prevent sensors from being repositioned while the structure is in use. This limits many conventional monitoring systems to a fixed configuration in which only certain portions of the structure can be monitored, in only certain ways. It is therefore also desirable to develop structural health monitoring systems capable of operating in cryogenic, high vibration environments in a flexible and adaptive manner, so as to be able to detect and assess structural failures and other problems at different locations in real time, without need for repositioning sensors.